A rotary loop taker is a device that must be incorporated into all lock-stitch sewing machines. Perhaps 70 to 80 percent or more of all industrial sewing machines are of the lock-stitch type, and therefore utilize a rotary loop taker. Lock-stitch sewing machines of the type described are especially useful for sewing canvas, leather, or other heavy materials.
The conventional loop taker is precision machined of fine steel to accurate proportions and balance throughout its extent from its weighted hub to its fragile hook or "loop seizing point." It is a costly item, and a short-lived item under the heavy wear and tear that accompanies the use of a typical industrial sewing machine. Conventional loop takers have a life of only three to six months, depending on the many variables involved.
Because no one prior to applicant has understood how to construct a rotary loop taker with a detachable loop seizing point that is a satisfactory device, conventional loop takers are currently constructed--as they have been for more than 60 years--with the loop seizing point formed integrally with a substantially circular frame member and with a crosswise extending frame support member as well. This of course requires that when either the loop seizing point or the initial portion of the bobbin case raceway that is an important part of the rotary loop taker has become damaged, the entire loop taker must be discarded.
The most vulnerable part of the fragile loop seizing point of a rotary loop taker is the tip. The tip can, for example, be chipped by the needle of the sewing machine, or burred by the friction that is created by the high speed revolutions of the loop taker as it picks up the thread off the needle. Since a faulty hook or loop seizing point tends to skip stitches, it must be repaired or replaced whenever its fragile loop seizing point accidentally breaks or becomes too dull through normal wear.
With a rotary loop taker of the usual type, most factories simply discard the entire device when the loop seizing point (which as pointed out is conventionally an integrally formed part of the loop taker) becomes chipped or otherwise rendered unusable. Others send the rotary loop taker to a facility that reprocesses the tip of the loop seizing point at great time loss. Either expedient is very costly.
The advantages that would be provided by a rotary loop taker with a detachable loop seizing point that could be readily removed and replaced with a new point were recognized at least six decades ago. Dickson U.S. Pat. No. 1,431,380, issued Oct. 10, 1922 on an application filed Jan. 25, 1921, attempted to provide such a loop taker. However, for reasons to be discussed below, the loop taker disclosed in that patent was unsatisfactory, and so far as is known to applicant was never practiced commercially. Until applicant made his novel and important invention, no one so far as applicant is aware even developed a loop taker with a replaceable loop seizing point that satisfactorily met the extremely demanding conditions for use with known sewing machines. For this reason, until applicant's invention the extremely urgent need for loop takers with replaceable loop seizing points had never been successfully met despite the attempts by Dickson (and others discussed below who pursued alternative approaches) to produce such a device.
Loop takers of the conventional type are customarily provided with a circular raceway around the inner wall to accept a bearing rib located on the exterior of the bobbin case. It has long been recognized that with use this raceway invariably becomes flawed--especially in the initial portion of the raceway, which is the most vulnerable to damage--and in this condition restricts the free passage of the thread around the bobbin case. As a consequence of such damage to the raceway and resulting restriction of free passage of the thread, thread breakages frequently result. When this condition occurs, the entire rotary loop taker of conventional construction must be totally replaced.
Still another troublesome condition that results from the wearing of the bobbin case raceway in the conventional rotary loop taker is known in the industry as "slop." This condition is the excessive "play" between the bobbin case and the inner wall of the loop taker which defines the bobbin case raceway.
"Slop" interferes with the proper release of the top thread (i.e., the needle thread) from around the bobbin case, and increases the incidence of jamming between bobbin case and raceway. It also tends to cause large, undesirable loops of top thread to be formed on the bottom of the material being sewed, because of the premature closing of the escape exit for the top thread. It may also cause the top thread to break, if a bunching of thread occurs because of the degree of "slop" that is present. Finally, if the "slop" is great enough to produce serious jamming of the top thread, the upper ledge of the bobbin case raceway on the loop seizing point may be broken as the operator manipulates the bobbin case in an attempt to free up the jammed thread.
Shortly before the above mentioned Dickson patent issued, another patent was granted (Smith U.S. Pat. No. 1,415,268, issued May 9, 1922) that contained a good discussion of the problem in a revolving hook machine of replacing a damaged loop seizing point that is integrally formed with the rest of the rotary loop taker (page 3, lines 76-119). That patent attempted to solve the problem referred to by providing a vertically laminated hook in which the tip is secured to the rest of the hook by a set of screws and can be removed and replaced as required. (The term "vertically laminated hook" is used in this specification to refer to a loop seizing point that is laminated in layers that are parallel to the shaft of the rotary loop taker.) The device disclosed in the Smith patent was thus a detachable loop seizing point of an entirely different type from applicant's detachable hook.
Loop seizing points of vertically laminated construction unavoidably present cracks in which the needle thread loop can get caught, either in the operation of the sewing machine in a forward direction or (as is more or less common for certain purposes) in the reverse direction. Such laminated devices also present other cracks in which lint and dirt can be trapped. In addition, a vertically laminated loop seizing point is inherently weaker, and usually possesses less total mass and thus provides a less solid construction, than an integrally formed loop seizing point. Finally, some specialized hooks are so thin in the radial direction with respect to the annular supporting frame that vertical lamination is not feasible.
Despite these disadvantages, the approach of vertical lamination has been followed, ever since the Dickson patent was issued, in all but two industrial detachable loop seizing point patents that are known to applicant. Examples of detachable loop seizing points that are fabricated in vertically laminated form are the devices that are disclosed in the patents to Corrall et al. U.S. Pat. No. 2,002,172 issued May 21, 1935, Joseph U.S. Pat. No. 2,495,637 issued Jan. 24, 1950, Corey U.S. Pat. No. 3,140,681 issued July 14, 1964, Corey U.S. Pat. No. 3,223,060 issued Dec. 14, 1965, and Kuhar U.S. Pat. No. 3,465,700 issued Sept. 9, 1969.
The only prior art patents issued after the Dickson patent for rotary loop takers with detachable loop seizing points for use in an industrial sewing machine that do not follow the lamination approach that are known to applicant are Grabowski U.S. Pat. No. 3,139,050, issued June 30, 1964 and Thiermann German Pat. No. 933,601, issued Sept. 29, 1955. The detachable loop seizing point disclosed in the former patent is designed to be used with a sewing machine having a take-up device (ordinarily of the roller type) that is located below the bobbin case of the machine. So far as applicant is aware, the invention of the Grabowski patent has never been practiced with a lock-stitch sewing machine in which the take-up device (ordinarily of the link or rotary type) is located above the bobbin case of the machine.
Indeed, the complicated and expensive construction of the Grabowski detachable loop seizing point is entirely unsuited for use with a sewing machine in which the take-up device is located above the bobbin case, because of (1) the danger of interference with the exit of the needle thread from around the bobbin case that would be presented in such a sewing machine by any device such as the Grabowski device that includes a finger extending forward from the base of the loop seizing point; (2) the danger of the needle thread getting caught in the sharply constricted V-shaped throat portion 68 of the Grabowski type detachable loop seizing point if used in such a sewing machine; and (3) the basic difficulty, or even impossibility, of removing a damaged loop seizing point of this type from any such sewing machine of conventional construction by maneuvering it through the cramped spaces surrounding the rotary loop taker as the operator attempts to effect "the pivotal movement of the beak member 60" that is called for by the patent (col. 3, lines 12-13).
Although the Thiermann detachable loop seizing point is of integral rather than laminated construction, it has other shortcomings that render is impractical to use.
The patent to Abresky U.S. Pat. No. 2,491,022, issued Dec. 13, 1949, attempts to meet the problem of replacing a damaged loop seizing point by still another expedient, in which the hook tip is not detachable at all but is simply cut off when worn, broken or otherwise damaged. This patent discloses cutting off the damaged tip, replacing it by brazing a new tip of wear-resisting carbide to the hook, and then finish-grinding the brazed tip for smoothness. This is obviously a cumbersome, time-consuming and expensive method.
The loop taker of this invention overcomes all the disadvantages of the prior art discussed above.